Fluff making method



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FLUFF MAKING METHOD Original Filed April 18, 1947 5 Sheets-Shoot 5@AMWQQ W @275 United States Patent FLUFF MAKING METHOD William H.Burger, Neenah, Wis., and Walter Wayne Wheelhouse, Glendale, Mo.,assignors, by mesne assignments, to Kimberly-Clark Corporation, acorporation of Delaware Original application April 18, 1947, Serial No.742,392, now Patent No. 2,689,985, dated September 28, 1954. Divided andthis application January 29, 1953, Serial No. 334,050

7 Claims. (Cl. 19156) This invention relates to a fluff making method.The fluff referred to is a product made by disintegrating paper orpapermakers pulp so as to convert the material into a mass ofindependent fibres or small pieces which may embody a plurality offibers in a single piece. Such disintegrated material is known and hasbeen used for various purposes such as the preparation of absorbent andother pads. The material may also be used in the formation of insulationblankets, packaging materials such as padding, and other products.

The main object of the invention is to provide a method wherebypapermakers pulp, paper, paperboard or like material may be efiicientlyconverted into fluff and into a web or pad of fluff material in whichform it may be employed for making pad-like products, or any otherproducts for which fluff may be suited.

Another object of the invention is to provide a method whereby the fluffproduced will be of substantially uniform fineness and whereby the webor pad produced from the fluff will be very soft and of substantiallyuniform softness and thickness throughout its area.

Other objects and advantages of the invention will be understood byreference to the following specification and accompanying drawingssheets).

lo the drawings:

Fig. 1 is a more or less diagrammatic view illustrating typicalmechanism employed for initially breaking down or disintegrating a webof papermakers pulp;

Fig. 2 is an end view in which parts have been shown in section toreveal certain details of construction of apparatus for acting on theinitially disintegrated material to complete its conversion into thedesired fluff, the plane of Fig. 2 being represented by the line 2-2 inFig. 4;

Fig. 3 is a plan view of the mechanism illustrated in Fig. 2;

Fig. 4 is a section on the line 4-4 of Fig. 2;

Fig. 5 is a section on the line 55 of Fig. 2 but on a reduced scale,

Fig. 6 is a plan section of the line 6-6 of Fig. 4; and

Figs. 7 and 8 are sections respectively on the lines 77 and 8-8 of Fig.4.

Paperrnakers pulpboard is a corse paper product which somewhat resemblesordinary blotting paper. Such pulpboard is well adapted to conversioninto fluff because of the convenience with which the pulpboard may behandled and its low cost. Such pulpboard is supplied in rolls such asrepresented at 1 in Fig. 1 and the web 2 of the material (or scrap,clippings and other primary or recovered fibre material of suitablecharacter) is suitably fed from the supply roll to a hammer mill 3 whichis suitably actuated by any conventional means (not shown). For somepurposes, the pulpboard may be moistened with water or other liquids orit may have wax or other material suitably applied to it by means ofspraying or dipping, or by means of applicator rolls such as representedat 4 in Fig. 1. However, the application or other treatment of thepulpboard before being fed into the hammer mill 3 is not essential.

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The outlet 5 of the hammer mill 3 is connected to a suitable blower 6which may be also actuated by any power source (not shown), thepartially disintegrated pulpboard being discharged through the conduit 7which extends from the discharge port of the blower 6.

The conduit 7 carries the initially disintegrated material to the inletport 8 (Figs. 3 and 6) of an attrition mill 9 which acts on thepartially disintegrated material to break it down to the required fibreor fibre-like condition. From the attrition mill 9, the fibre-likematerial is discharged downwardly into the hood or forming chamber 10(see Fig. 4) which is arranged over a foraminous belt 11 so that thefibre-like material will be deposited on the belt 11 to form a web orpad of the required thickness. The belt 11 is, of course, propelledcontinuously so as to deliver a finished pad from beneath the hood 10,the finished pad being transferred to a discharge conveyor 12 and thenceto other mechanism for winding the pad on itself or otherwise treatingor acting on the pad.

The attrition mill 9 consists of a pair of concentric, oppositelyrotated plates or discs 13 and 14 (Fig. 6) which have their adjacentfaces provided with cooperating grinding plates 15 and 16, respectively.The grinding plates 15 and 16 may each be formed in sections arrangedcontinuously or in relatively spaced relation and their cooperatingfaces may be cut to provide various forms of ribs or ridges. The typegenerally known as rapid-cut serrated plates give good results undermost conditions.

The discs 13 and 14 with their plates 15 and 16 are rotated in oppositedirections by means of suitable electric motors 17 and 18 on the shaftsof which the said discs are directly mounted. Provision is desirablymade for adjusting the rotors 13 and 14 toward and from each other sothat the spacing indicated at 19 between their grinding plates 15 and 16may be varied to suit conditions incurred in operation. With certainkinds of papermakers pulp, the clearance 19 between the grinding plates15 and 16 should be about five thousandths (.005) of an inch, but thisclearance may be reduced or increased to produce the desired results.The closer the plates are to each other, i. e., the less clearanceprovided, the finer will be the fluff discharged from the mill. Thefineness of the fibre, that is to say, the degree of disintegration ofthe pulpboard, is also determined to some extent by the character of theridges on the plates 15 and 16. In general, the finer the ridges, thegreater will be the disintegration of the pulp.

As shown in Fig 6, the rotor 14 is a solid, plate-like member whereasthe rotor 13 has its hub 20 connected by spoke-like elements 21 to theperipheral portion of the rotor. The rotor 13 is also preferably formedwith a smooth-walled inlet opening or mouth portion 22 whichcommunicates with the port 8 to receive the initially disintegrated pulpfrom the conduit 7. Moisture, preferably in the form of dry steam, maybe injected into the initially disintegrated pulp through a steam pipeline 23 which communicates at 24 with the inlet port 8 so as todischarge moisture into the air-borne stream of fibrous material.

The steam is delivered under considerable pressure (for example, 50 to60 pounds per square inch) and the jet of steam is advantageouslydirected toward the inside of the wall of the rotor mouth 22 so as toprevent the adherence of fibres thereto incident in part to centrifugalforce. Stoppage of the month by accumulated fibre is thereby prevented.If the addition of moisture is not desired at this point, for example,if moisture is supplied elsewhere or not required, a jet of air mayreplace the jet of steam.

The attrition mill 9 and the driving motors 17 and 18 are suitablysupported on a framework 25 (Fig. 4), which is provided with suitablecross members and other parts for also supporting the forming hood 10,conveyor 11 and other parts of the apparatus.

The disintegrated paper pulp delivered by the conduit 7 to the inlet ofthe attrition mill is caused by centrifugal force to pass between thecooperating grinding plates 15 and 16 of the mill to be thereby brokendown to fibre-like form. The plates of the attrition mill may be soadjusted into such proximity to each other as to cause the pulp fedthereto to be discharged in the form of separated, substantiallyindividual fibres, or the adjustment may be such that the dischargedmaterial will be in the form of fibre-like pieces embodying severalfibers bound together. To produce a very light and well puffed-up fluffweb, it is desirable that the discharge mate rial'be very fine but it isnot essential that the pulp material be actually broken down intoindividual fibre form if that is ever actually accomplished.

The conduit 7 and all other paths through which the disintegratedpulpboard is caused to flow in the described apparatus are desirablymade smooth walled and streamlined, i. e., free from recesses,projections and the like which would tend to trap any of thedisintegrated material. The rotors 13 and 14 of the attrition mill areenclosed in a suitable metal casing which embodies outer side members 26and 27 of metal and a metal circumferential band 28, and a bottomdischarge opening represented at 29 (Fig. 4) is provided in the casing.The casing comprising the said parts 26, 27 and 28 is preferably linedwith smooth surfaced material, the said lining being so arranged as toprovide the desired smooth. nontrapping enclosure. Examples of suitablematerial for the lining are glass and synthetic glass-like sheeting,such as typified by commercially available Lucite." Othersmooth-surfaced materials may, of course, be employed, it being thepurpose to prevent the disintegrated fibres from attaching themselveseither mechanically or electrically to any of the surfaces with whichthey come in contact. Electrical attachment is preventable by propermoisture conditioning of the fibre and also, to some extent, by the useof lining material which is electrically non-conducting.

To promote the How of the initially distintegrated material from theattrition mill and to deposit the material discharged from the hammermill in the desired manner on the travelling screen 11, a large volumeof air is caused to travel downwardly through the attrition millchamber. The volume of air is controlled so that its action on thefibers, and its fibre-depositing effect can readily be adjusted toobtain the required fluff deposit on the travelling belt 11.

Air flow through the attrition mill housing or chamher 9 is induced bymeans of a blower 30 (Figs. 2, 3, and which may be driven by an electricmotor or the like indicated at 31. The blower 30 discharges a column ofair into an upwardly extending conduit 32 which is here represented asbeing of rectangular cross-section. At its upper end, said conduit 32has two laterally extending branches 33 and 34, the branch 33 leading toa downwardly extending hopper-like member 35 which communicates with theupper end of the attrition mill casing 9 as best shown in Figs. 2 and 4.The branch 34 connects with a downwardly extending conduit 36 whichexhausts to the outside atmosphere through a suitable dust trap 360which prevents any entrained fibre or fluff material from beingdischarged into the atmosphere.

The volume of air flowing through the attrition mill housing has animportant bearing on the characteristic of the fluff material producedby the apparatus, and the said air volume is adjustable or controllableby means of an adjustable vane or valve plate 37 located in therectangular riser 32 as best shown in Figs. 2 and 5. The vane 37 ishinged at its upper end as indicated at 38 so as to be pivotallyadjustable toward and from opposite sides of the riser 32 to divide thecolumn of air into separate columns which respectively enter thebranches 33 and 34. Adjustment of the vane 37 may be convenientlyeffected by means of a handle 39 secured to the pivot shaft 38 whichcarries the vane. Any suitable means (not shown) may be provided forlocking the handle 39 and the vane 37 in selected position ofadjustment.

As will presently appear, some of the air flowing through the apparatusis recirculated, and it will be seen that control of the volume orvelocity of the air through the attrition mill housing and formingchamber is attained, at least in part, by regulation of the air columnswhich are directed into the branch 33 and outlet or discharge connection36.

The hood 1!] previously referred to constitutes the upper portion of achamber into which the disintegrated pulp is directly discharged by theattrition mill 9. Said hood is supported on a horizontally disposedrectangular frame structure 40 which is in turn supported by suitablyarranged main frame portions as represented in Fig. 4. said horizontalframe 40 is provided with suitable lining plates 41 which extend fromthe upper edges of the respective sides of the frame structuredownwardly to a point closely adjacent the conveyor belt 11 except tothe extent that the liner plate 41a at the discharge side of saidchamber has its lower edge spaced upwardly from the said conveyor agreater distance as indicated. A vertically adjustable sealing roll 41bis provided to more or less iron the issuing fluff web to uniformthickness as desired.

In said frame structure 40 there are rotatably mounted a series ofshafts 42 which extend across the frame, the shafts being rotatablymounted in suitable bearings 43 carried by said frame 40. Said bearingsare sealed in any Well known manner to prevent the entrance of any ofthe fluff material into said bearings. The shafts 42 are, in thisinstance, arranged in pairs, there being four pairs respectivlelydesignated, a, b, c, and d (Fig. 4). The shafts 42 of the pairs a and bare driven in a counterclockwise direaction as viewed in Fig. 4, thepair a being driven by means of a belt 44 and the pair b being driven bya belt 45. The belts 44 and 45 cooperate with suitable pulleys on theshafts 42 and with suitable pulleys on the driven shaft of an electricmotor 46 (Figs. 2 and 3) which is mounted on the main frame structure25.

The shafts 42 of the pairs 0 and d are driven in a clockwise directionas viewed in Fig. 4 by means of belts 47 and 48 which cooperate withsuitable pulleys carried by the shafts and suitable pulleys carried bythe driven shaft of an electric motor 49 which, like the motor 46 issupported by the main frame structure 25.

Each of the shafts 42 is equipped with a series of plates or bars 50 and51, the said plates being of elongated form, and the plates 50 beingdisposed with their lengths extending transversely of the lengths of theplates 51. The plates 50 and 51 of adjacent shafts 42 are staggered sothat when the shafts rotate, the plates of one shaft will not engage theplates of another shaft but will pass each other side by side as shownin Fig. 8. The arrangement of plates 50 and 51 on the shafts 42 iscontinuous across the entire length of each shaft so that the fluffmaterial descending in the chamber formed by the hood 10 and the frame40 must pass through the screen-like bed formed by the multiplicity ofplates 50 and 51 on the shafts 42. These shafts are driven at a highrate of speed so that any collection of fibres can practically neverpass through the said bed without being subjected to the breaking actionof the plates of one or more of the rotating plate-carrying shaftswhich, for convenience, have been designated by the term whizzel-s."

The fibrous material after passing through the whizzers is deposited onthe screen conveyor 11 which is pro pelled continuously by means of asuitable electric motor 52 (Figs. 2 and. 3) which, in this instance,directly drives the conveyor pulley 53 and thereby the conveyor hand 11.Suitable means is provided for adjusting the speed at which the conveyoris driven so as to thereby permit adjustment of the depth of the fibrousmaterial which will be collected on the conveyor belt and carried out ofthe depositing chamber under the edge of the lining plate 41a. Suchspeed-controlling means may consist of a variable speed motor 52 or anyother desired equipment of which many are well known. In some instancesit may be preferred to deposit the fibrous material directly on a web ofcreped tissue or other paper. T 0 that end there is provided a suitablesupporting stand 54 on one side of the mechanism for supporting a roll55 of the desired paper, and guide rolls 56 for guiding the paper web 57into place on the conveyor 11 as it enters the fluff-depositing chamber.A suitably driven feed belt 550 or other means may be provided foreffecting delivery of the web to the screen belt 11.

In other instances, it may be preferred to deposit the fibre directly onthe belt 11 and to transfer the deposited web of fibres from the belt 11to a paper web. For this purpose, a suitable stand 58 may be providedfor supporting a roll 59 of the desired paper or other material, the webof material from the roll 59 being drawn upwardly and over the receivingend of another conveyor 12. In that case, the web 60 of fluff can bestripped from the foraminous belt 11 by means of a transfer plate .61which also serves to deliver the web of fluff to the conveyor 12 or to aweb 62 on said conveyor 12.

The foraminous conveyor belt 11 which passes under and forms the bottomof the depositing chamber, has its upper reach supported by means of aforaminous member 63 which may consist, for example, of a sheet ofexpanded metal. Said sheet of expanded metal is supported by arectangular frame 64 which is slightly longer and wider than therectangular frame 40 forming the lower portion of the depositingchamber, and said frame 64 is in turn supported by main frame portions25 provided for that purpose. To further support the foraminous member63, a plurality of cross members 65 extend from side to side of theframe 64, these supports being preferably in the form of invertedV-shaped members as represented in Fig. 4 so as to avoid any reductionin the area of air passageways through the supporting member 63.

A hood 67 is formed below the frame 64 and suitably connected therewithas shown in Figs. 2 and 4 to provide a receiver for the air passingdownwardly from the depositing chamber and through the conveyor 11 andsupporting member 63. Said hood 67 is provided with an outlet 68 at oneside which is connected by means of a suitable conduit 69 to the inletport of the blower 30 (see Fig. 2). The blower 30 is in a continuousflow air conduit or circuit wherein air is forced out of the dischargeend of the blower through the conduit 32 into the branch conduit 33 andthence into the attrition mill housing 9 and downwardly through theforming chamber formed by the hood and frame 40, through the foraminousconveyor 11 and foraminous supporting member 63 into the hood 67 andback through the conduit 69 to the blower 30.

The arrangement of the whizzers (the shafts 42 and plates 50 and 51) intwo oppositely rotating sets is such that these sets tend to spread thedownward flow of fibre toward the ends of the forming chamber from thecentral portion thereof. This detail helps to secure even distributionof the fluff or fibre and the deposition of a uniform layer of fiufl onthe travelling conveyor. The fluff is, of course, somewhat forcefullydeposited on the travelling conveyor incident to the air current whichcarries the fluff downwardly, and this is so even though a web of crepedtissue or like paper 57 is first placed on the conveyor belt. The web ofpaper 57 will, of course, be quite porous as typified by creped tissuepaper so that the air flow may continue at a sufficient velocity toproduce the desired fibre deposition on the paper web.

The vane or deflector 37 should preferably be adjusted so that a slightvacuum will be maintained in the forming chamber. In the arrangementdescribed, this is quite practicable by discharging an adequate portionof the air column through the discharge branches 34 and 36 byappropriate adjustment of the said deflector. It will be seen that theblower 30 is capable of withdrawing from the forming chamber through theconveyor belt, the hood 67 and the conduit 69 more air than is fed intothe attrition mill through the conduit branch 33 when a sufficientportion of the withdrawn air is discharged to the atmosphere through thesaid discharge branch 34-36. Pivotally adjustable deflectors representedat 33a in the conduit branch 33, augmented by series 33b and 330 ofdeflectors or dividers, afford a desirable control of the air flowthrough the branch conduit 33 and into the attrition mill 9. Byappropriately positioning and adjusting these deflectors, substantiallyuniform dispersion of air currents through the housing of the attritionmill and into the forming chamber 10 can be effected.

The fiow of the air-borne fibre from the attrition mill into the formingchamber may be further controlled by opening or closing openings such asindicated at 10a (Figs. 2 and 4) in the forming chamber hood. Byregulation of such openings, the flow of fibre may be directed towardthe central axis of the chamber which is between the two banks ofwhizzers. The fibres are then exposed to repeated action of the whizzerswhich tend to throw the fibres towards the opposite ends of the chamber.Complete breaking of any clots of fibres is thereby assured.

Although the forming chamber is preferably maintained under a slightvacuum, it should nevertheless be understood that the arrangement issuch that a very high volume of air is maintained in the forming chamberin relation to the weight of fluff therein. The constant discharge ofair from the circulating system is required to attain the indicatedpressure control, because of the entrance of air into the system byleakage, especially at the forming screen, and because of the constantsupply of air from the hammer mill 3 and its associated blower 6.

In the production of a soft and uniformly deposited web of fluffmaterial, it is desirable that the fiber-to-air ratio in the formingchamber be very low. A fiber-to-air ratio in that chamber of about 1.5percent by weight, i. e., a weight ratio of about 1.5 to 100, or evenless produces very desirable results for certain products. This ratiomay be considerably lower and higher to produce acceptable products forvarious purposes. The moisture content and other characteristics of thefibre, the density of the desired product, its thickness, and otherfactors enter into the determination of the most suitable fibre-to-airratio for production purposes.

About 15 pounds of pulp can be processed per minute with therecirculation of about 7000 cubic feet of air per minute in theillustrated apparatus in which the bottom dimensions of the forming hoodare of the order of 60 inches in length and 30 inches in width, thelength being in the direction in which the forming conveyor 11 travels.This air volume and screen size indicate an air velocity of the order of500 feet per minute through the forming screen, but it may be observedthat because of the expanding form of the chamber, this velocity islower than that in the narrow upper portion of the forming chamber 10.The said volumes of pulp and recirculated air indicate a fiber-to-airweight ratio of slightly less than 3 to 100.

The whizzers in the illustrated embodiment of apparatus areapproximately 10 inches in diameter, and they are driven at a high rateof speed such as 1800 revolutions per minute. They are preferablylocated as near to the forming wire as possible without disturbing orpreventing the fluff formation on the forming belt or conveyor 11, thepurpose of maintaining a close relationship between these parts beingthat of preventing re-clotting of the fibres which have passed throughthe Whizzers, and which fibres it is desired to deposit in theirseparated form.

In apparatus of the illustrated proportions, there should be a pressuredrop between the forming chamber above the forming wire 11 and thesuction chamber below the same of from 2 to inches of water, and it maybe in the range of from 1 to inches of water. Such a pressurerelationship will insure the passage of the necessary amount of airthrough the forming area on the belt and the deposition of the separatedfibres at the required rate for continuous operation of the apparatus.The higher the pressure differential, the closer can be the relationshipbetween the whizzers and the forming area. Moreover, the higher pressuredifferential will result in faster movement of the separated fibres todeposited position on the forming belt, thereby aiding in preventingfloating or migrating of the fibres toward each other into clotted orbunched condition.

In the described apparatus, steam has been referred to as being injectedfor moistening purposes. Other moistening means may be employed such asadding steam at the hammer mill entrance opening, spraying water on thepulpboard before it enters the hammer mill or humidifying the air beforeadmitting it to the hammer mill. Also, the air which is recirculated inthe apparatus may be humidified by any of the methods just indicated.However, the injection of steam into the attrition mill as illustratedis a very satisfactory manner of accomplishing the addition of moisture.Such steam does not merely moisten the fibres but also serves tohumidify the air and serves as a conducting medium for transferring thecharges on the fibres to the metal walls of the conduits which aregrounded. This prevents static electricity from accumulating on thefibres and the fibres from being attracted to each other and to thewalls of the conduits on which they might otherwise tend to collect witha tendency to close the conduits. Proper moistening of the fibressubstantially eliminates adverse electrical effect and nonconductingconduits may be substituted for metal conduits if desired.

In addition to lining the attrition mill with smooth surfaced materialsuch as glass or glass-like materials, plywood sheeting, stainlesssteel, etc., the walls of the forming chamber 10 and the lining plates41 and 41a of the horizontal frame 40 are also preferably made ofsimilar smooth surfaced materials so as to prevent as far as possibleany adhesion and collection of fibres on those surfaces. Transparentglass-like material is preferably used for forming the walls of theforming chamber 10 so that the fibre formation can be readily observedand steps promptly taken to prevent any clotting tendency which maydevelop from time to time under varying operating conditions.Atmospheric temperature and humidity have some effect as do also thecharacteristics of the pulp being disintegrated and converted intofluff. Any pronounced tendency for fibre to collect on the walls of theforming chamber would be readily noticed, and it would, of course. beapparent that similar accumulation would be started on other passagewaysthrough which the fibre is com ducted. Hence, the operators would bepromptly forewarned of the need for the taking of steps to discourageand prevent such fibre accumulation.

The characteristics of the fluff web produced by the machine, especiallythe bulkiness or thickness of the web is influenced to a considerableextent by the pressure differential on the forming wire. The lower thispressure differential, the greater will be the bulk and softness of thefiutf web formed.

The air-formed fluff web resulting from operation of the describedapparatus is useful in many fields of which absorbent pads for bandagesand other purposes, filters, insulation packing, etc., are examples. Forapplication in these various fields, the density, thickness, and othercharacteristics of the web may require changing, and such changes caneasily be effected by varying the pressure differential above and belowthe forming wire, the spacing of the cooperating plates of the attritionmill, the ratio of fibre-to-air in the system, the speed at which theforming wire 11 is driven, and/or the mesh of said wire or a paper webthereon and other possible variables. The apparatus is capable offorming a 30-inch wide web of fluff material A; inch thick at a speed ofthe order of 200 feet per minute. Greater speeds, for example 400 feetper minute may be attained under some circumstances and depending inpart on the thickness and density Of web desired, inherent capacity ofthe machine, character of the fibre, and other factors.

In instances where fine disintegration of the fibrous material is notrequired, and where the fibrous material supplied to the apparatus is ofsuch character that it may be easily disintegrated, passage of thematerial through a single disintegrator such as a hammer mill or anattrition mill may be sufficient. In some instances, a hammer mill maybe substituted for the attrition mill in the arrangement described.

Instead of mounting the attrition mill plates directly on the motorshafts, the mill plates may be belt or otherwise driven from the same orfrom separate motors.

The Whizzers above referred to as being about 10 inches in diameter maybe smaller or larger, if desired. Whizzers having a diameter of 6 incheshave been successfully used.

This application is a division of our copending application, Serial No.742,392, filed April 18, 1947, now Patent No. 2,689,985 issued September28, 1954 and entitled Fluff Making Method and Apparatus.

Various other changes in the described construction may be made whileemploying the principles of the apparatus as described, and withoutdeparting from the invention as set forth in the following claims.

We claim:

1. The method of making a loosely felted web of fibrous material whichcomprises the steps of producing an airborne stream of fibres in whichthe weight ratio of fibres to air is less than 10 to 100, and in whichthe velocity of the stream is of the order of 500 feet per minute,screening the fibre out of the stream, and subjecting the stream to amechanical fibre-clot breaking and fibre spreading operation in advanceof and in such proximity to said screening operation that the fibertravel distance between said operations is so short that the fibers aresubstantially provented from converging and forming slots during theirtravel between said operations, and maintaining the air pressure in saidstream below surrounding atmospheric pressure.

2. The method of making a loose-1y felted web of fibrous material whichcomprises the steps of producing an airborne stream of fibers in whichthe weight ratio of fibres to air is within the range of from 1 up to 3to 100, and in which the velocity of the stream is substantial,screening the fibre out of the stream, and subjecting the stream to amechanical fibre-clot breaking and fibre spreading operation in advanceof and in such proximity to said screening operation that the fibertravel distance between said operations is so short that the fibers aresubstantially prevented from converging and forming clots during theirtravel between said operations, and maintaining the air pressure in saidstream below surrounding atmospheric pressure.

3. The method of making a loosely felted web of fibrous material whichcomprises the steps of producing an airborne stream of fibers having afiber-to-air weight ratio which is less than 10 to 100, subjecting thestream to a screening operation by which the fibers are collected inlayer form on a screen, causing the stream to flow at a velocity ofaround 500 feet per minute through the screen, and subjecting the streamto a fiber-clot breaking and fiber dispersing operation over an areawhich is approximately coextensive with the screening area and inadvance of said screening operation but in such proximity thereto thatthe fiber travel distance between said operations is so short that thefibers are atforded but little opportunity to converge and clot duringtheir travel between said operations.

4. The method of making a loosely felted web of fibrous material whichcomprises the steps of producing an air borne stream of fibres in whichthe weight ratio of fibres-to-air is within the range of from about 1 upto about 3 to 100, screening the fibres out of the stream by directingsaid stream at a substantial velocity under the action of a pressurediflerential against a travelling foraminous member, and subjecting thestream to a mechanical fibre-clot breaking and fibre spreading operationin advance of and in such proximity to said screening operation that thefibre travel distance between said operations is so short that thefibres are substantially prevented from converging and forming clotsduring their travel between said operations.

5. The method of making a loosely felted web of fibrous material whichcomprises the steps of producing an air borne stream of fibres in whichthe fibre-to-air weight ratio is about 1 /2 to 100, screening the fibresout of the stream by directing said stream at a substantial velocityunder the action of a pressure differential against a travellingforaminous member, and subjecting the stream to a mechanical fibre-clotbreaking and fibre spreading operation in advance of and in suchproximity to said screening operation that the fibre travel distancebetween said operations is so short that the fibres are substantiallyprevented from converging and forming clots during their travel betweensaid operations.

6. The method of making a loosely felted web of fibrous material whichcomprises the steps of producing an air borne stream of fibres in whichthe fibre-to-air weight ratio is sufficiently low that the fibre contentof the stream is highly diluted, directing said stream at a substantialvelocity against a travelling foraminous member while maintaining apressure differential between the opposite sides of said foraminousmember, thereby forcefully de- 10 positing said fibres on saidforaminous member, subjecting the stream to a fibre-clot breaking andfibre spreading operation in advance of and in such proximity to saidforaminous member to cause the fibrous material to reach said member asseparated substantially individual fibres and/or fibre-like pieces, andmaintaining the air pressure on both sides of said foraminous memberbelow sur rounding atmospheric pressure.

7. The method of making a loosely felted web of fibrous material whichcomprises the steps of producing an air borne stream of fibres in whichthe fibre-to-air weight ratio is within the range of from about 1% toabout 3 to 100, directing said stream at a substantial velocity againsta travelling foraminous member while maintaining a pres suredilferential between the opposite sides of said foraminous member,thereby forcefully depositing said fibres on said foraminous member,subjecting the stream to a fibre-clot breaking and fibre spreadingoperation in advance of and in such proximity to said foraminous membarto cause the fibrous material to reach said member as separatedsubstantially individual fibres and/ or fibrelike pieces, andmaintaining the air pressure on both sides of said foraminous memberbelow surrounding atmospheric pressure.

References Cited in the file of this patent UNITED STATES PATENTS2,152,901 Manning Apr. 4, 1939 2,195,158 Watts Mar. 26, 1940 2,230,880Brown Feb. 4, 1941 2,319,666 Drill May 18, 1943 FOREIGN PATENTS 294,079Germany Sept. ll, 1916 422,226 Great Britain Jan. 8, 1935

